Process for obtaining pure nitric acid from nitrous gases



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stares WERNER SIEBER'I, 0F LAUFENBURG, AARGAU, SVIITZERLAND, ASSIGNOF;T0 NI RUMI AKTIENGESELLSCHAFT, OF ZURICH. SWITZERLAND, A CORPORATION OFSWITZEE- LAND.

PROCESS FOR OBTAINING PURE NITRIC ACID FROM NITROUS GASES.

No Drawing. Application filed May 13,

To all whom it may concern:

lie it known that l, .Wnnsnn SIEBERT, a citizen of the Republic ofGermany, residing at Laufenburg, Aargau, Switzerland, have inventedcertain new and useful Improvements in. a Process for Obtaining luncNitric Acid from Nitrous Gases, of which the followin is aspecification.

In manufacturing nitric acid by means of the electric arc,disintegration of the material of the electrodes carrying the arc occursto some degree, and the material separated is then carried off by thegas-current in form of a very fine powder. During the process of theabsorption of the nitrous gases obtained through the arc; this linepowder is diss lved in the nitric acid and contaniinatcs the latter tosuch an extent as to make it inore. or less useless for technicalpurposes. Such impurities are especially undesirable when ironelectrodes ane employed, because nitric acid for technical use shouldonly con tain a particularly low percentage of iron. Now it has beenfound that the solution of such impurities in the nitric acid can easilybe prevented if the absorption of the nitrous gases takes place at asuilicient-ly low tern-- perature as at about zero degrees centigrade orbelow, and if the result-ant acid is im inediately passed throu h a linefilter. In this manner a clear acid practically free of iron isobtained, containing but a few hund redths of a gram of impurities tothe liter. In order to maintain the desired temperature during the timeof absorption, it is necessary to abstract all the reaction heat cahscdby the transformation of N0 into H3 0 and moreover the mixture of oxygenand nitrogen gases must be sutliciently cooled, because this mixture,after leaving the electric furnace and the directly coupled boiler andcooler, has a temperature that is far above 0 C. It has been found to be1922. Serial No. 560,727.

l especially advantageous to effect this cooling down by feeding theabsorption towers through which the nitrous gases pass with nitric acid,which itself is kept at 0 C. or below in coolers placed outside thetowers, so that there is no higher temperature in any portion of thesystem. Only in this manner it is possible to prevent the solution ofthe line powder thrown off from the electrodes. The resultant nitricacid is then passed through a very tine filter, without previousheating, thus giving a pure acid.

l. A process for obtaining pure nitric acid from nitrous gasescontaining irnpurities in form of a tine powder, in which the nitrousgases and the nitric acid are kept in all parts of the absorption systemat a temperature about 0 so that solution of the impurities in thenitric acid is prevented, and in which the undissolved in1- purities aresubsequently removed.

2. A process for obtaining" pure nitric acid from nitrous gasescontaiiingimpurities in form of'afine powder, in which the nitrous gasesand" the nitric acid are kept in all parts of the almorption system at atemperature not above zero degrees centigrade thus preventing solutionof the impurities in the nitric acid, and inv which the impurities areremoved by filtration.

3. A. process for obtaining pure nitric acid from nitrousgase'scontaining impurities in form of a fine powder, in which the absorptiontowers are supplied with cooled nitric acid for keeping the nitrousgases and the nitric acid in all parts of the absorption system at atemperature of about 0 C. so that solution of the impurities in thenitric acid is prevented, and in which the undissolved impurities aresubsequently removed.

In testimony whereof I atiix my signature.

DR. WERNER SIEBERT.

